1. Field of the Invention
The present invention relates to an automotive alternator, and in particular, relates to the construction of a stator coil of an automotive alternator for suppressing damage to the insulation coated on the coil wire by eliminating three-dimensional twisting of the coil wire and for improving productivity.
2. Description of the Related Art
FIG. 11 is a cross-section showing a conventional automotive alternator.
A conventional automotive alternator includes: a Lundell-type rotor 7 mounted so as to rotate freely by means of a shaft 6 within a case 3 consisting of an aluminum front bracket 1 and an aluminum rear bracket 2; and a stator 8 secured to the inner wall of the case 3 so as to cover the outer circumference of the rotor 7.
The shaft 6 is rotatably supported by the front bracket 1 and the rear bracket 2. A pulley 4 is secured to one end of the shaft 6 to enable rotational torque from an engine to be transmitted to the shaft 6 by means of a belt (not shown).
Slip rings 9 for supplying electric current to the rotor 7 are secured to the other end of the shaft 6, and a pair of brushes 10 are housed in a brush holder 11 disposed within the case 3 so as to slide in contact with the slip rings 9. A regulator 18 for regulating the magnitude of an alternating voltage generated in the stator 8 is affixed by adhesive to a heat sink 17 attached to the brush holder 11. A rectifier 12 electrically connected to the stator 8 for rectifying an alternating current generated in the stator 8 to a direct current is mounted within the case 3. This rectifier 12 is provided with a plurality of diodes 24 arranged on a heat sink 19, and a circuit board 25 for electrically connecting each of the diodes 24 and forming predetermined circuits.
The rotor 7 includes: a rotor coil 13 for generating magnetic flux by passing electric current therethrough; and a pair of pole cores 20 and 21 disposed so as to cover the rotor coil 13 in which magnetic poles are formed by the magnetic flux generated by the rotor coil 13. The pair of pole cores 20 and 21 are made of iron, each has a plurality of claw-shaped magnetic poles 22 and 23 projecting from an outer circumferential edge thereof spaced at even angular pitch circumferentially, and the pole cores 20 and 21 are secured to the shaft 6 facing each other so that the claw-shaped magnetic poles 22 and 23 intermesh. In addition, fans 5 are secured to both axial ends of the rotor 7.
The stator 8 includes: a stator core 15; and a stator coil 16 composed of wire wound around the stator core 15 in which an alternating current is generated by changes in the magnetic flux from the rotor 7 as the rotor 7 rotates.
In an automotive alternator constructed in this manner, an electric current is supplied from a battery (not shown) by means of the brushes 10 and the slip rings 9 to the rotor coil 13, and the magnetic flux is generated. The claw-shaped magnetic poles 22 of the pole core 20, are magnetized to N polarities by the magnetic flux, and the claw-shaped magnetic poles 23 of the pole core 21 are magnetized to S polarities by the magnetic flux. At the same time, the rotational torque of the engine is transmitted to the shaft 6 by means of the belt and the pulley 4, and the rotor 7 is rotated. Thus, a rotating magnetic field is imparted to the stator coil 16 and electromotive force is generated in the stator coil 16. This alternating electromotive force is rectified to a direct current by means of the rectifier 12, its voltage is regulated by the regulator 18, and the battery is recharged.
Next, the stator coil construction applied to a conventional automotive alternator will be explained with reference to FIG. 12. Moreover, FIG. 12 is a partial enlargement of a conventional stator viewed from the inner circumferential side.
The stator core 15 is formed into a cylindrical shape and a plurality of slots 15a whose grooves extend in the axial direction are disposed at even angular pitch around the circumference thereof so as to be open on the inner circumferential side. The stator coil 16 is constructed by connecting into one unit the starting end wires (or the finishing end wires) of three coils respectively corresponding to three phases prepared by inserting wire in a wave shape successively into every third slot 15a. Moreover, the slots 15a into which the strands of wire of each of the three coils are inserted are offset from those of each of the other coils by one slot. Further, the wire extends axially outwards from the slots 15a and constitutes front-end and rear-end coil end portions 16a and 16b.
Next, the construction of the stator coil 16 will be explained in detail.
Coil segments 30 are formed by shaping strands of copper wire coated with insulation into a general U-shape, and as shown in FIGS. 13 and 14, each includes a pair of straight portions 30a, a pair of oblique portions 30b each bent from a straight portion 30a and extending in a straight line, and a return portion 30c joining the pair of oblique portions 30b by twisting and bending the wire so as to turn back around.
Now, the coil segments 30 are inserted from the rear end into pairs of slots 15a three slots apart. At this time, the coil segments 30 are inserted into the slots 15a such that the strands of wire are folded back at the return portions 30c, from the inner circumferential side to the outer circumferential side, for example. Then, the straight portions 30a of the coil segments 30 projecting towards the front end from the slots 15a are bent circumferentially outwards, as shown in FIG. 15, and the ends thereof are additionally bent parallel to the straight portions 30a. Next, adjacent ends of the coil segments 30 are joined to prepare one phase of the coil. At this time, the adjacent ends of the coil segments 30 are stacked radially and joined, and constructed such that the strands of wire appear to be folded back from the inner circumferential side to the outer circumferential side at the joined portions.
The other two phases of the coil are prepared similarly. For each of the phases of the coil, the slots 15a into which the coil segments 30 are inserted are offset by one slot from each of the other phases.
The stator coil 16 is constructed by connecting the three phases of coil prepared in this manner in a three-phase alternating-current connection such as a Y connection or a delta connection.
In the coil end portions 16a and 16b of a stator coil 16 constructed in this manner, because the wire is formed so as to bend back from the inner circumferential side to the outer circumferential side at the apex, adjacent strands of wire are neatly arranged in the circumferential direction in the vicinity of the apexes, as shown in FIGS. 17 and 18. Moreover, FIG. 17 is a diagram showing an example of a wire array in a rear-end coil end portion, and FIG. 18 is a diagram showing another example of a wire array in a rear-end coil end portion. By adopting constructions of this kind, the coil end portions become practically the same shape around the entire circumference, improving alignment.
Moreover, in the above conventional example, all of the straight portions 30a projecting towards the front end from the slots 15a were bent circumferentially outwards, but some of the straight portions 30a projecting towards the front end from the slots 15a may be bent circumferentially inwards and the tips thereof additionally bent parallel to the straight portions 30a, as shown in FIG. 16.
A conventional stator coil 16 applied to an automotive alternator is constructed by inserting the straight portions 30a of many generally U-shaped coil segments 30 into predetermined slots 15a, bending the straight portions 30a projecting from the slots 15a circumferentially in the vicinity of the end surface of the stator core 15, additionally bending the tips of the straight portions 30a parallel to the axial direction of the stator core 15 at the connecting position, and joining the tips of the straight portions 30a to form connections.
Thus, bending and twisting is applied to the strands of the stator coil 16 both before and after insertion into the slots, increasing damage to the coil, as well as increasing the number of production steps and reducing productivity.
Furthermore, because the coil segments 30 are in close proximity to each other when inserted into the slots 15a, the bending operation is made difficult after insertion, reducing productivity.
Because the return portions 30c of the coil segments 30 are formed into a three-dimensional twist, insulation is easily damaged during formation of the coil segments, giving rise to electrical faults, and tolerance of physical contact between adjacent coil strands is low.
Furthermore, due to the need to accurately insert the coil segments 30 into predetermined positions within the slots 15a, a high degree of machining precision has been required in the coil segments 30, particularly in the twisting of the return portions 30c, making work difficult. In addition, the coil segments 30 are chucked after insertion in order to bend the tips of the coil segments, but because the shape of the coil segments 30 is difficult to chuck, the chucking is unstable, and there is a risk of damaging the teeth of the stator core 15 during the process of bending the coil segments circumferentially after insertion.
Furthermore, in the coil array shown in FIG. 18, because it is necessary to position one of the straight portions 30a of a coil segment 30 in the radially outermost position within a slot 15a and the other straight portion 30a in a position one row inwards from the radially outermost position within a slot 15a three slots away and insert them parallel to the axial direction of the stator core 15, it is difficult to insert many coil segments 30 simultaneously, reducing productivity. This is considered to be due to the fact that the coil segments 30 have no portions suitable for chucking because the regions of the oblique portions 30b and return portions 30c of the coil segments 30 have complex shapes, and also to the fact that the pitch and degree of parallelism between pairs of straight portions 30a cannot be formed with high precision.
Additionally, because the coil segments 30 are arranged in an unstable state in close proximity to each other when inserted in the slots 15a, it is difficult to weld the tips of the coil segments 30 to each other, making work time long and increasing costs.